Guided tissue regeneration is a surgical procedure intended to restore or regenerate the morphology and function of tissues or organs that were destroyed by disease or trauma. In tissue regeneration, the regenerating tissues have to repopulate the same site and space previously occupied by the healthy tissues that were destroyed. Furthermore, to restore the morphological and functional relationships between the different regeneration tissues at the regeneration site, the repopulation of the affected site and the subsequent differentiation of the repopulating cells should be an orderly and concerted process.
The technique of GTR aims to allow orderly and concerted repopulation of an affected site by regenerating tissues. To this end, a barrier is interposed between the regenerating tissues and the tissue that might intervene with the regenerative process. The barrier is maintained in place until the affected site is repopulated by the proper tissues and the regenerating tissues reach maturity.
Membrane barriers are currently used mainly in dentistry, for GTR of regenerating periodontal tissues that were destroyed by periodontal disease or trauma. Generally, two types of membranes are in use, membranes made of non-degradable material and membranes made of degradable materials.
Collagen are a family of proteins with a well determined triple helical configuration. Among these proteins, collagen Type I is most prevalent, constituting approximately 25% of the body's proteins and 80% of the connective tissues' proteins. Collagen Type I polymerizes to form aggregates of fibers and bundles. Collagen are continuously remodeled in the body by degradation and synthesis. Collagen Type I is degraded only by a specific enzyme--collagenase, and is resistant to any non-specific proteolytic degradation.
Collagen is a weak antigen and most of its antigenicity resides in the non-helical terminals of the molecule. These terminals may be removed by enzymes such as pepsin. Its weak antigenicity and its relative resistance to degradation make collagen a good candidate as a building material of implantable devices.
A molecular solution of type I collagen can be prepared from a connective tissue rich in this protein and the molecular collagen can then be reassembled into fibrils which can then combine to form a collagen matrix. Collagen matrices can be molded in vitro into numerous implantable devices such as, for example collagen sheets, collagen tubes, etc.
When used to form implantable devices, collagen matrices should maintain their integrity for long periods of time. The resistance towards degradation of the collagen fibrils can be increased by increasing the number of intermolecular cross-links. Several agents, such as aldehyde fixatives and imides, and treatments such as radiations have been used to achieve this purpose. The main drawbacks of such treatments are toxicity and inability to accurately control the degree of cross-linking.